1 files changed, 5 insertions, 3 deletions
diff --git a/mltt/core/elaborated_statement.ML b/mltt/core/elaborated_statement.ML
index 33f88cf..2e129c8 100644
--- a/mltt/core/elaborated_statement.ML
+++ b/mltt/core/elaborated_statement.ML
@@ -95,12 +95,14 @@ fun inst_morphism params ((prfx, mandatory), insts') ctxt =
     (*instantiation*)
     val instT =
       (type_parms ~~ map Logic.dest_type type_parms'')
-      |> map_filter (fn (v, T) => if TFree v = T then NONE else SOME (v, T));
+      |> map_filter (fn (v, T) => if TFree v = T then NONE else SOME (v, T))
+      |> TFrees.make;
     val cert_inst =
       ((map #1 params ~~ map (Term_Subst.instantiateT_frees instT) parm_types) ~~ insts'')
-      |> map_filter (fn (v, t) => if Free v = t then NONE else SOME (v, cert t));
+      |> map_filter (fn (v, t) => if Free v = t then NONE else SOME (v, cert t))
+      |> Frees.make;
   in
-    (Element.instantiate_normalize_morphism (map (apsnd certT) instT, cert_inst) $>
+    (Element.instantiate_normalize_morphism (TFrees.map (K certT) instT, cert_inst) $>
       Morphism.binding_morphism "Expression.inst" (Binding.prefix mandatory prfx), ctxt')
   end;